In mammography systems the most commonly used compression device includes a compression paddle which is parallel to an image detector on a bucky and the paddle is moved vertically relative to the bucky with a patient's breast therebetween to compress the breast. The compressed breast is then exposed to x-rays to obtain a mammography image on a film or on a digital detector such as a semi-conductor detector. Compression of the breast enables better x-ray imaging because the breast is thinner, the breast tissue is spread, there are fewer superimposed layers of tissue in the image. The breast is usually most thick at the chest wall and thinner at the anterior nipple end and a substantial difference in compression results between the posterior and anterior breast portions with less force and compression at the thinner anterior portion. The imaging quality of the less compressed breast suffers.
It has been recognized and proposed in several devices to supplant the known system for other non-parallel paddle systems such as disclosed in U.S. Pat. No. 5,506,877; U.S. Pat. No. 5,706,327 and in a paddle being sold by American Mammographics of Chattanooga, Tenn. These prior art proposals have a number of serious shortcomings which will become apparent from the following discussion relative to compression of the breast in a mammography operation. The posterior breast portion may be more denser and/or more thick at the chest wall than at the nipple end, or there may be a breast implant at the chest wall, or pectoral muscle that interferes with a proper compression of the posterior portion of the breast.
A mammography system is most effective, in detecting lesions in fatty breasts and is the least effective in very dense breasts. In some tests it appears that the sensitivity to detection of the presence of a benign lesion or malignant lesion drops almost in half where the breast is extremely dense. That is, a progressive decrease in mammography sensitivity results as the breast density increases. Furthermore, often the majority of the missed cancers are located in the middle of the breast where the compression with the parallel technique above described using a conventional, horizontal compression paddle because there is relatively less compression at the middle portion and also at the anterior portion than at the chest wall portion of the breast. Often the lesions or calcites are closely adjacent to the chest wall and may be superimposed close to the chest wall. If these superimposed calcites are not spread or, if they are pushed back into the chest wall out of the imaging area, the chance of a cancer being missed will be greatly increased.
To improve the image quality so that cancers will not be missed, there is a need to lesson imaging deficiencies such as an unsharpness of the lesion, poor contrast of the lesion, and a failure to spread apart the fiberal glandular tissues to show superimposed portions of the lesions. Inadequate compression appears to be the underlying cause of many of these imaging deficiencies and a better improved compression should prevent the unsharpness by reducing breast thickness to allow shorter exposure times and a loss of sharpness due to the motion of the patient while in the mammography machine.
With respect to resolution or contrast, there is a minimal standard of being able to see eleven pairs of lines per millimeter. It has been reported that Residents or others being trained in the art of viewing mammography images find them difficult because of the relatively poor image quality and because the responsibility for failure to detect the cancer has serious result and a misdiagnosis of a benign area causes the patient to be brought back for further mammography or biopsies. Hence, the image details that need to be interpreted are very essential to the initial decision as to whether the breast is normal or abnormal and if it is abnormal, to require further action between the patient and doctor.
The prior art American Mammography paddle is a rigid paddle that has no rotating or swinging parts but has a gently curved compression surface that slopes downward towards the nipple. As the paddle is lowered the curved compression surface is said to contact the breast between the chest wall and the anterior portion. The rigid inclined posterior portion of the paddle as illustrated in FIG. 4 of this application has a horizontal force component that pushes posterior breast tissue into the chest wall and from the imaging area. Another problem with the non-rotatable American Mammography paddle is that it is difficult for the operator to use in that the operator cannot readily insert the operator's fingers between this lowered compression surface and the underlying bucky in order to grip the breast and pull it away from the chest wall because of the large downward force at the anterior end of this rigid paddle surface. The paddle actually grips the operator's fingers as the breast is pulled and reduced in thickness allowing the anterior end of this rigid paddle to pinch the inserted fingers. This makes it too difficult to shift or spread the tissue manually during the breast compression. More specifically, an operator will pull the breast away from the chest wall with the operator's fingers as the breast is being compressed to prevent tissue from being pushed back into the chest wall and from the imaging area. The inserted fingers are caught by the further downward shifting of the paddle's nipple end as the pulled breast reduces in thickness under this manual pulling.
Because the operators are under typical production quotas in the mammography offices where the mammographies are performed, the operators may not insert their fingers to pull tissue forwardly where the American Mammography paddle is used. The mammography production desired by many most offices is to take four views per patient within a period of about 15 minutes, so that approximately four patients per hour are run through the mammography machines.
Now there has been a general recognition that good and more uniform compression is most desirable in mammography systems, as also a recognition that the proposed systems should address the issue of less patient's discomfort because many of the patient's find the mammography operation to be painful. The operator usually pushes the patient toward the machine such that the chest is brought tight against the downwardly moving paddle and close to the ribs. It is because most of the cancers that occur are often located adjacent the chest wall. Such cancers are closer to the lymph nodes.
The proposal of a paddle disclosed in U.S. Pat. No. 5,506,877 is that of a paddle that has not been commercially marketed and has not been viewed in the market place even though the patent application was filed in November of 1994 and granted in April of 1996. It has several embodiments. It is stated that the paddles of these embodiments compress the breast and push the tissue away from the chest wall and into the imaged volume. This may occur initially but when the angled portion 48c (FIG. 8A) and the curved portion (FIG. 4) adjacent the chest wall are pivoted downwardly to compress the anterior and middle breast tissue they will push the posterior breast tissue into the chest wall and from the imaged volume. The embodiment illustrated in FIG. 3 of the patent has a tray with an upwardly, vertically extending chest wall part 48b on the tray and a hinged breast portion 48a which overlies the top of the breast and which is hinged at 52 and is pulled downwardly by a motorized mechanism. In this FIG. 3 embodiment, the hinge 52 which is located right at a critical area of the chest wall where most of the lesions are found. The vertical chest wall part 48b has a lower, thin edge that engages and compresses the breast along a thin straight line, which although not a knife edge, applies the vertical compressing over a very narrow thin line area. High breast compression at such a thin area of the breast may cause some considerable pain because the tissue is unable to stretch, as will now be explained.
With the conventional horizontal paddle, the breast is often over-compressed at the posterior portion of the breast in order to compress the middle and anterior regions of the breast. In order to get the anterior portion sufficient compression in these women, the operator keeps moving the paddle downwardly until there is such pain that the patient demands that the compression cease. It is not uncommon in this instance, that a red line or even a blood blister is seen at the top of the breast after the breast is removed from the machine. The red line is the result of hemorrhaging or breaking of capillaries.
It has been discovered that such pain is not the result of the compression of this posterior breast tissue beneath the skin, but it is the result of tearing of the skin which does not stretch substantially. As the chest wall end of the paddle slides down the chest wall, the skin located several centimeters from the chest wall must slide back under the descending posterior end of the paddle. The problem is that in order to get sufficient compression at the middle and anterior portions of the breast, the operator having already compressed the posterior sufficiently for good imaging, further lowers this paddle corner until sufficient compression of the anterior region is achieved. It is this last downward movement that the pain is most severe and which is a result of the tearing of the skin as the hemorrhaging occurs. By way of specific example only, if the posterior paddle descends 6 centimeters and achieves sufficient posterior compression for good imaging and the operator lowers the posterior paddle corner another three centimeters to obtain sufficient middle and anterior compression, this additional displacement causes the pain due to tearing of the displaced, non-stretchable skin. The apparatus and method of the present invention overcomes the above-described problem by achieving sufficient compression of the middle and anterior breast tissue to hold the tissue against pushing back into the chest or displacement of skin and tissue from the chest wall without the displacement of the skin that causes the pain and/or skin tearing. This is achieved by lowering the preferred paddle to compress the anterior breast portion sufficiently to hold the chest wall tissue against displacement inwardly and to achieve good imaging, e.g., 6 centimeters in this example, and then swinging only the anterior portion of the paddle down to compress the anterior breast portion while the posterior end of the paddle remains stationary and does not descend the additional three centimeters that caused the pain and red line formation. In a paddle embodiment illustrated and described herein, the posterior paddle end extends horizontally for about two centimeters and this provides sufficient area across the posterior breast to apply the desired initial posterior breast compression without pushing the posterior breast tissue towards the chest wall and from the imaging area as illustrated in FIG. 4. After this chest wall compression by lowering the paddle, e.g., at 6 centimeters, then the operator swings a middle and anterior breast portions downwardly to compress the anterior and middle breast portions sufficiently for good imaging. The amount of force applied at the anterior end is from a spring force biasing the anterior paddle portion downwardly in one embodiment and by an operator controlled motor drive in another embodiment. In the former case, if the operator desires to further compress the middle or anterior breast portions, the operator may apply additional pressure by manually swinging the inclined portion further in the downward direction and then locking the anterior portion in this position while imaging the breast. This additional anterior compression is done without shifting further downwardly the posterior paddle end with a concomitant and further displacing the skin at the chest wall thereby resulting in additional pain or discomfort to the patient.
Returning to the paddle 48 disclosed in U.S. Pat. No. 5,506,877, this paddle 48 is rotatable in several directions by having the first pivot 52 and a second pivot 58. The latter is a centrally located pivot axis and is used to pivot the entire paddle for axilla-inferior imaging of the breast.
Also, Adamkowski et al., U.S. Pat. No. 5,706,327, discloses pivoting about a centrally located pivot axis and in this patent the compression force at the chest wall has a horizontal component pushing posterior tissue toward the ribs and from the imaging volume or area. This patent claims that the paddle is substantially horizontal with respect to the detector at imaging and hence does not recognize that the heel effect problem of imaging of the anterior breast can be alleviated by pivoting the anterior end of the bucky, and the detector thereon, into an angled, non-parallel relationship with respect to the paddle, which will be described in greater detail hereinafter in relationship to the description of an embodiment of the invention.
The present invention also addresses the problem of how to readily and inexpensively retrofit existing mammography machines to improve the quality of imaging and provide less discomfort to the patient. The paddle system illustrated in U.S. Pat. No. 5,506,877 employs a complicated, expensive motor drive and sensor system to drive the hinged portion downwardly to compress the anterior breast portion. Many, if not most owners of existing machines will be reluctant to pay for and to install such an extensive motor drive and sensor retrofitting of their machines. It is stated in this patent that the operator may manually pull the hinged portion downwardly to compress the middle and anterior breast portions. Neither way of operation provides a paddle assembly having an internally biased hinged section that is merely released to compress the breast with desired compression force as is done in one embodiment of the invention. Where an automated paddle drive is desired, the paddle can be driven, as discussed hereinafter with another embodiment of this invention.
There is a need for an improved system that provides good compression across the posterior, middle and anterior breast portions to improve imaging and a need to reduce discomfiture of the patient.